The Portal (Downtown Rail Extension)

Alignment

The Portal, also called the Downtown Rail Extension (DTX), would carry Caltrain about 2.2 miles from its current terminus at 4th & King into downtown San Francisco, ending in the two-level trainbox already built beneath the Salesforce Transit Center. California High-Speed Rail would later use the same route. The line runs mostly underground beneath Townsend Street and then north beneath Second Street before curving east into the trainbox. About 1.05 km would be mined tunnel under Townsend and Second, using sequential excavation from two access shafts, and the remaining underground structures would be cut-and-cover. The tunnel would carry two tracks, widening to three near the Transit Center.

The project includes a new underground station at Fourth & Townsend, with a concourse one level below the street and a two-track platform two levels down. It also fits out the Transit Center trainbox with six tracks and three center platforms for commuter and high-speed trains. The Transit Center connects with eight transit operators and is a block from Embarcadero BART. TJPA projects about 90,000 riders a day. Panels on the west side of the trainbox leave room for a possible future second Transbay rail crossing.

Updates

2026-11 — State awards $750 million

CalSTA awarded The Portal $750 million from the Transit and Intercity Rail Capital Program on November 10: $100 million in Cycle 8 for preconstruction work and $650 million for construction under a multi-year agreement. The award depends on a federal Full Funding Grant Agreement (FFGA). TJPA says the money will help it secure the $3.38 billion federal Capital Investment Grant share. Approval and award of the preconstruction contract are expected to run into spring 2027, with construction readiness targeted for 2029 and passenger service in December 2036.

2026-06 — Cap-and-invest money in doubt

In May the Metropolitan Transportation Commission endorsed $750 million in state cap-and-invest funds for The Portal, but the money was at risk while the California Air Resources Board renegotiated state funding. TJPA’s executive director said staff would go to Sacramento to secure it.

2026-02 — San Francisco funds engineering; about $2.2 billion still needed

San Francisco County Transportation Authority staff recommended $12.5 million in local Prop L sales-tax funds for the project’s FTA Engineering-phase work. The memo put the remaining funding need at about $2.2 billion, of which about $1.05 billion is expected from state sources. It said Caltrain service would start in 2036, depending on completing the funding plan.

2025-12 — Tunnel contract moves to the proposal stage

TJPA issued the request for proposals for the 40-CT progressive design-build contract, covering the tunnel and other civil works, to the teams shortlisted in the earlier qualifications round. It is also advancing right-of-way acquisition.

2025-07 — Cost estimate revised to $7.57 billion

TJPA’s board received an indicative update putting the capital cost at $7.57 billion, or $6.84 billion excluding the completed trainbox. The update reflected planned changes to the project configuration and new escalation assumptions. The 2023 estimate had been $8.25 billion ($7.52 billion excluding the trainbox).

2024-08 — $2.75 billion funding gap delays the federal agreement

A board report showed a funding gap of about $2.75 billion. Against an $8.25 billion cost, FTA had committed $3.384 billion and TJPA had identified $1.39 billion from local, regional and state sources. TJPA said it could not close the gap in time for an FFGA in October 2024. It identified $541 million in possible value-engineering savings and scope cuts, including dropping an eastward extension of the trainbox toward Beale Street. AECOM was hired as program and construction manager.

2024-05 — FTA advances project to Engineering

The Federal Transit Administration admitted The Portal to the Engineering phase of its Capital Investment Grant program and set the project’s federal share at $3.38 billion. To receive the money, TJPA must close the funding gap and sign an FFGA.

2018 — Transit Center trainbox completed

The roughly 160,000-square-foot underground trainbox beneath the new Salesforce Transit Center was finished in 2018. It has sat empty since, waiting for The Portal to bring trains in.